Onrosuses eat all manners of vegetation, but their favorite food by far is watermelon. At dusk they emerge from the water to graze on grasses, and look for more tasty snacks. Young onrosuses who are more adventurous will sometimes try to steal food from the castle's gardens. They seldom succeed, because onrosuses can neither move quietly nor hide behind anything. Despite being less than talented at stealth, onrosuses do hide their eggs extremely well. Their eggs are actually buried in mud, so they're practically impossible to find. Several adult onrosuses remain near these eggs at all times, ready to chase off intruders. Another aggressive act takes place whenever two males are in the water at the same time. They become very territorial, and snort angrily at one another. Sometimes a chase begins. Despite being incredibly large and heavy, onrosuses can run for short distances very quickly. Otherwise, males are friendly towards other males. As far as anyone can tell, onrosuses have no particular social order. Their groups can be anywhere from a few to one hundred. Interaction is no different between males and females. As for telling the two genders apart, they are similar in size, but only males bear sharp tusks.

It's not difficult to find a onrosus. They seldom wander far from water, where their favorite pastime is to wallow in mud to keep cool. Despite spending the majority of their days submerged in water, onrosuses are not great swimmers. They are too heavy. Instead, they simply sink to the bottom, where they search for tasty plants to eat. Onrosuses can hold their breath for surprisingly long amounts of time, and can remain underwater for several hours. They move by kicking at the ground beneath them, which propels them forward in strange hops. Even the smallest onrosus is born knowing how to swim, and takes to the water at any sign of danger. Of course, there aren't many animals who would dare to attack an onrosus. They are huge creatures, and males have tusks that can easily rip through skin and even armor. While onrosuses were once heavily hunted for their tusks, they managed to defend themselves quite well. An onrosus has a very powerful bite, and can crush bone with just one snap. They have also been known to sit on animals who anger them. It's simple to tell if an onrosus is enraged – they paw at the ground and lower their heads threateningly. Should one ever see this occur, it's best to turn and slowly back away.